This invention relates to a method for providing enhanced blood circulation. More particularly this invention relates to a method for providing enhanced blood circulation, including circulation, microcirculation, and venous return by the application of intermittent pneumatic compression (IPC) in selected pre-determined time cycles.
Intermittent pneumatic compression is the technique of cyclically compressing a limb with air pressure to enhance the circulation of blood. Pressure is applied from a source of compressed air by a control mechanism that intermittently inflates a cuff enveloping all or part of an arm or leg. Parameters that can be controlled in known IPC techniques include the rate of pressurization, the pressure achieved, the rate of depressurization, and the rest duration between pulses. As disclosed in U.S. Pat. No. 5,496,262, assigned to the common assignee and incorporated herein by reference, IPC can also be applied by means of cuffs having more than one chamber, the chambers being disposed at relatively distal and proximal locations along the limb. Additional parameters that can be controlled with multiple-chambered cuffs include the level of pressure that can be provided to each chamber (i.e., graduated compression), and the timing of the application of pressure to each chamber (i.e., sequential compression).
IPC is known to be of therapeutic benefit for a variety of circulatory disorders. For example, the use of IPC is known in the prevention and treatment of edema. IPC is also known as a means for reducing the risk of deep vein thrombosis (DVT). U.S. Pat. No. 5,588,955, also assigned to the common assignee and incorporated herein by reference, discloses a method and apparatus for applying graduated and/or sequential IPC to a limb to prevent DVT. Applicant""s assignee also manufactures and sells devices under the trademarks VENAFLOW(copyright) and ARTERIOFLOW(trademark) which are used to apply IPC to a patient in need of such therapy.
As disclosed in the aforementioned U.S. Pat. Nos. 5,496,262 and 5,588,955, in IPC as used in the prior art the period of compression is typically short, about ten seconds, and the recovery period between pulses is about a minute, to allow the veins to refill after being emptied by the short pulse of compression. The optimal amount of compression known in prior art devices is in the range of 35-45 mmHg. Further, it is known that the velocity of venous flow during the period of compression is generally proportional to the rate of pressurization. For example, a pulse that reaches maximum pressure in six seconds will have a much greater effect on venous velocity than a pulse that reaches the same maximum pressure in 30 seconds.
Prior researchers studying the effects of IPC on DVT prophylaxis have recommended continuous application of IPC. Nicolaides et al., in xe2x80x9cIntermittent sequential pneumatic compression of the legs in the prevention of venous stasis and postoperative deep venous thrombosis,xe2x80x9d published in Surgery, vol. 87, No. 1, pages 69-76, January, 1980, at p. 75 suggested that IPC that was started from the induction of anesthesia and continued until 16-24 hours after an operation was effective in preventing DVT during the time it was applied; and further that a sequential compression device might be even more effective if used for several days during the postoperative period, if not continuously, at least intermittently. In a study by Salzman et al., xe2x80x9cEffect of Optimization of Hemodynamics on Fibrinolytic Activity and Antithrombotic Efficacy of External Pneumatic Calf Compression,xe2x80x9d published in Ann. Surg., vol. 206, no. 5 November 1987, pp. 636-641, patients undergoing surgery were treated with IPC as prophylaxis for DVT until they became ambulatory, roughly 3 weeks. Clagett, et al., in xe2x80x9cPrevention of Venous Thromboembolism,xe2x80x9d Chest, vol. 108, no. 5 October 1995 Supplement, pp.3125-3345, suggest at p. 3185 that IPC devices must be applied either intra-operatively or as soon as is feasible post-operatively and worn continuously except during ambulation. At page 3195 it is suggested that DVT prophylaxis be provided for at least 7 to 10 days post-operatively. In xe2x80x9cProphylaxis against Deep Vein Thrombosis after Total Knee Arthroplasty,xe2x80x9d by Westrich, et al., J. Bone and Joint Surgery, vol. 78-A, no. 6 June 1996, a device for providing pulsatile pneumatic plantar compression was found to be effective for preventing DVT if applied post-operatively for 96 hours for a mean of 19.2 hours per day. The Handbook of Venous Disorders, 1996, in Ch. 17, xe2x80x9cCurrent recommendations for prevention of deep vein thrombosis,xe2x80x9d by Heit, states at p. 296 xe2x80x9cIPC should be initiated preoperatively and continued until the patient is fully ambulatory. The utility of IPC is limited by patient intolerance and noncompliance, non-use during periods of physical therapy, and unsuitability for continued home use after hospital discharge.xe2x80x9d
In addition to the known effect of DVT prophylaxis, it recently has been learned that IPC also can have an effect on microcirculation in skeletal muscle distant from the site of direct IPC application. Microcirculation is discussed in the text The Return of Blood to the Heart, A. M. N. Gardner and R. H. Fox, second ed., Chapter 3, xe2x80x9cMicrocirculatory Blood flow.xe2x80x9d A mechanism for this effect is proposed by Liu, et al., in xe2x80x9cThe Effect of Intermittent Pneumatic Compression of Microcirculation of Distant Skeletal Muscle,xe2x80x9d presented at the 43rd Annual Meeting, Orthopaedic Research Society, Feb. 9-13, 1997, San Francisco, Calif., which suggests that IPC creates shear stress on the vessel wall which may induce release of nitric oxide (NO) from vascular endothelial cells, producing systemic dilatation of vessels. This hypothesis was supported in Liu, et al., xe2x80x9cNitric oxide: A Possible Regulator of Vasodilation in Distant Skeletal Muscle Induced by Intermittent Pneumatic Compression,xe2x80x9d presented at the 44th Annual Meeting, Orthopaedic Research Society, Mar. 16-19, 1998, New Orleans, La., wherein the relationship between the IPC-induced vasodilatory effect in distal skeletal muscle and increasing NO release during compression was confirmed by studies using different dosages of N-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor.
It has been found, however, that the effect of IPC on microcirculation is not constant over the entire time during which IPC is applied. Thus, the effect of IPC measured as vasodilation, i.e., the increase in vessel diameter, has been found to peak after about 20-40 minutes of continuous IPC application, and to decrease thereafter, even while the application of IPC continues. It would be desirable to be able to continue vasodilation over a longer period of time than is currently possible with known IPC techniques.
It is thus one object of the invention to provide enhanced circulation, venous return, and microcirculation over a longer period of time than has been obtained by currently known IPC techniques.
In accordance with the invention, blood circulation, including circulation, microcirculation, and venous return, is enhanced by the application of IPC in a pre-determined pattern of periods of IPC applications alternating with recovery periods in which lesser or no IPC is applied. It has been found that, surprisingly, the use of a recovery period after a period of IPC application results in greater enhanced circulation subsequent IPC applications, over that which would have been observed in the absence of any recovery period. Use of the inventive method can also enhance microcirculation in skeletal muscle distant from the actual site of IPC application.